I'm bulding a new studio,now finishing with the isolation...,my first idea was to soffit the Genelec 1038B as main monitors but my initial budged was gone with the isolation...and no genelec possible

My idea is made a custom 3-way pasive main monitors I serched and find this posible speakers to use:
from the studio series
lows
12BR70 12"http://profesional.beyma.com/ENGLISH/producto.php
mids
6B30P 6.5"http://profesional.beyma.com/ENGLISH/producto.php
or
5MP60N 5"http://profesional.beyma.com/ENGLISH/producto.php
higs
T2010 1.25"http://profesional.beyma.com/ENGLISH/producto.php
filter
F300 http://profesional.beyma.com/ENGLISH/producto.php
for the mids which will better the 6.5 or 5" ?
any advise about the cabinet ?
for the 12" they recomended 50-120l enclosure ,but wich will be better larger or smaller ? vented or closed ?
thanks,
(and sorry for my english still learning.....)